In completing wells having production or injection zones which lie adjacent incompetent subterranean formations (i.e. formations formed of an unconsolidated matrix such as loose sandstone or the like) or which lie adjacent formations which have been hydraulically-fractured and propped, serious consideration must be given to the sand control problems which will almost certainly arise during the operational life of the well. These problems arise when large volumes of sand and/or other particulate material (e.g. backflow of proppants from a hydraulically-fractured formation) dislodge from the formation and become entrained in the formation fluids and are produced therewith into the wellbore. These produced materials are highly detrimental to the operation of the well and routinely cause erosion, plugging, etc. of the well equipment, which, in turn, leads to high maintenance costs, and considerable downtime of the well.
While many techniques have been proposed for controlling sand production in a well, probably the most widely-used is one which is generically known as “gravel packing”. Basically, a gravel pack completion is one wherein a fluid-permeable liner (e.g. screen, perforated liner, slotted liner, pre-packed screens, combinations thereof, or the like) is positioned within the wellbore (open or cased) adjacent the incompetent or fractured zone and is subsequently surrounded by aggregate or particulate material through some means of circulation (collectively called “gravel” or, more generally, “proppant”). As known in the art, the gravel particles are sized to block or filter out the formation particulates which may become entrained in the produced fluids while the openings in the liner are sized to block the gravel from flowing into the liner. This two-stage filtration system is commonly known as a “gravel pack”.
There are two basic, well-known techniques for installing a typical gravel pack completion in a wellbore. A first of these techniques involves positioning the fluid-permeable liner in the wellbore before placing the gravel around the liner to form the gravel pack. The other technique involves placing the gravel in the wellbore first and then driving, rotating, or washing the liner into the gravel to form the gravel pack.
While both of these techniques have been widely used, both require the circulation of fluid during installation. For example, where the liner is positioned first in the wellbore, a slurry of gravel and a carrier fluid may be pumped down and out through a “cross-over” sub into the annulus formed between the liner and the cased wall (cased hole) or the bore wall (open hole). The openings in the liner allows only the carrier fluid to flow from the annulus into the liner while the gravel is strained from the fluid and is deposited within the annulus to form the gravel pack. The gravel can also be placed by flowing the gravel directly into the annulus around the liner from the surface or through open-ended tubulars, which extend down the wellbore.
Where the gravel is placed in the wellbore first, the liner is lowered on a workstring and is washed or driven into place while fluid is being pumped down the workstring and out the bottom of the liner. This circulating fluid (i.e. jetting action) is necessary to “fluidize” the pre-positioned or preset gravel so that the liner can be lowered into and through the gravel to form the gravel pack. Unfortunately, since the fluid flows through the workstring, the pumping must be stopped each time an additional stand of workstring must be added to lower the liner further into the gravel. While the pumping is stopped, the gravel settles and in many instances, cannot be adequately “re-fluidized” upon the resumption of pumping to allow any deeper placement of the liner into the gravel.
Since both techniques require the pumping and/or circulation of fluid under pressure during installation, both may experience severe fluid loss problems, especially when used to complete zones adjacent formations having normal or below normal pressures or pressures which are below the hydrostatic pressure of the completion fluids in the wellbore. For example, in placing gravel around a preset liner, the loss of expensive completion fluids to an underpressured formation (i.e. formation having a pressure less than the fluid pressure in the wellbore) can be excessive. The use of known loss-circulation materials in the gravel slurry is limited since such materials severely hinder the placement of the gravel around the liner. Where the gravel is positioned first, the fluid losses during the high pressure jetting required to “fluidize” the preset gravel also can be excessive. In both cases, these fluid losses not only result in increased costs due to the loss of the expensive completion fluids, themselves, but also contribute to severe formation damage in many cases thereby reducing the productivity and/or operational life of the completed well.
To counteract the above-described problems, U.S. Pat. No. 5,036,920 disclosed a screen with an external auger to allow the gravel to be deposited without circulation, so as to minimize fluid loss. Thereafter, the screen was rotated into the gravel to form the gravel pack without the need to circulate to fluidize the gravel. Augers have been used on perforating guns to facilitate extracting them after they have been shot and debris collects in the annular space surrounding them. This use of an auger on a perforating gun is shown in U.S. Pat. No. Re. 34,451. In this reference, the well is brought in to remove debris from perforating and then gravel is spotted in position and then the slurry is pumped into the perforations. Another technique is to deposit the gravel after placing the screen and then use occasional vibration to evenly distribute the deposited gravel in the annulus.
One technique of gravel deposition and dispersal into the perforations is to use fracturing. The gravel is dispersed using high pressure and flow rates. Hydraulic fracturing techniques of various types are described in several U.S. Patents, such as: U.S. Pat. Nos. 3,933,205; 4,550,779; 5,228,510; 5,617,921; 5,598,891 and 5,669,448. Various sensors can be employed to monitor the fracture packing operation, as described in WO 02/06593 A1.
More recently deposition of gravel by fracturing has become more prevalent for exclusion of produced sands in areas prone to sand production. The reason for this shift in technique is the higher productivity realized with the fracturing technique. Fracturing effectively penetrates to hundreds of feet into the formation to bypass previously induced damage mechanisms. However, fracturing has brought on other problems such as crossover tool erosion, casing erosion, screen erosion, stuck crossover tools, downhole real time pressure monitoring problems and fluid losses to the formation.
The method of the present invention mitigates at least some of these prior problems. The gravel is placed in position after under-balanced perforating. Fracturing is done with the gun in position and the gun is subsequently extracted. The screen is inserted into the preset gravel that has been pushed into the perforations and augered into the gravel with the help of vibration. Subsequently, the vibrator is removed and a production packer is tagged into the screen for subsequent production. These and other aspects of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment, which appears below.